EVALUATION OF PRE-AND POSTRECONSTRUCTION COUNT-DEPENDENT METZ FILTERSFOR BRAIN PET STUDIES

In this study we evaluated pre-(PR-R) and post-reconstruction (PO-R) c ount-dependent Metz filters for PET brain studies in order to increase signal-to-noise ratio. A set of studies using a 3D Hoffman brain phan tom was performed at various count levels, and a reference image set w as created from extremely high count images. Several combinations of P R-R and PO-R filtering were considered to find the optimal means of pr ocessing, including: Hann filter alone; PR-R Metz filter without or wi th a PO-R low pass filter; and PO-R Metz filter without or with a PR-R low pass filter. A formula was established to correlate the optimal P O-R Metz filter order with the net counts. Resolution [full width at h alf-maximum (FWHM) and full width at tenth maximum (FWTM)I, normalized residual mean square differences (NRMSD) between the ideal and the pr ocessed images, noise reduction and contrast were used as parameters f or the evaluation of the different filter combinations. Resolution is decreased by all filter combinations that can effectively control nois e; however, FWTM increases less than FWHM. NRMSD indicates that the us e of Hann and (optimal) PO-R Metz filter is the most powerful combinat ion from among those tested. A close correlation (r=0.969) was found b etween the net counts and the optimal order of the PO-R Metz filter. A t the count levels of clinical studies the PO-R Metz filter was found to control noise much more effectively and enhance the contrast when c ompared to the routinely used Hann filter alone, and produced images o f better quality. (C) 1997 American Association of Physicists in Medic ine.